Methods using flow cytometers are generally known as methods for detecting hemocytes in blood and the tangible constituents found in urine and the like.
Flow cytometers analyze particles by irradiating particles flowing in a flow cell, and detecting optical information from the particles.
For example, flow cytometers provided with the optical system shown in FIGS. 1A and 1B are known (U.S. Pat. No. 4,577,964). The optical system shown in FIG. 1A is configured by a laser 101, beam separator 102, photodetector 103, a lens pair 106 including cylindrical lenses 104 and 104, obstacle 113 such as a wire or the like, microscope objective lens 115, opaque screen 117, lens 118, and photodetector 119. FIG. 1B shows the light path of the incident radiation from the laser 101 that has passed through the cylindrical lenses 104 and 105.
Light from the light source laser 101 is focused at points 112 and 114 by the cylindrical lenses 104 and 105. Point 112 is focused on the cells passing through the channel 107. Point 114 is focused on the wire 113. That is, the wire 113 blocks all the light from the lens pair 106 directly through the point 112. Thus, the direct light from the lens pair 106 is blocked by the wire 113. At point 112, the light scattered by the cells (scattered light) passes the wire 113 and reaches the microscope objective lens 115. The scattered light is collected by the objective lens 115 at the aperture 116 formed on the opaque screen 117. The aperture 116 is positioned in the center of the image plane of the objective lens 115. Therefore, only the scattered light passes through the aperture 116 and reaches the photodetector 119.
In recent years, demand has increased for compact analyzers provided with flow cytometers, for example, blood analyzers. In the optical system of the flow cytometer disclosed in U.S. Pat. No. 4,577,964, a space is required to dispose the light shielding member of the wire 113 between channel 107 of the flow cell and the microscope objective lens 115, which functions as a detecting lens. Therefore, the distance is lengthened between the channel 107 and the microscope objective lens 115. Moreover, a predetermined distance is required between the photodetector 119 and the microscope objective lens 115 to ensure a suitable optical magnification in the photodetector 119. This requirement resulted in problems inasmuch as the longer distance made the detector unit larger, as well as the particle analyzer itself.